The prior art relating to the preparation of aromatic amines may be exemplified by U.S. Pat. No. 2,750,416. However, this patent teaches an azomethine-phenol mechanism utilizing formimines which have been derived from amines possessing a tertiary alpha-carbon atom, that is, the azomethine reactant possesses an alkyl substituent wherein the carbon atom which is directly attached to the nitrogen atom is completely substituted by other alkyl groups. The two components of the reaction mixture are admixed in reacting proportions or, if so desired, an inert organic solvent such as naphtha, benzene, or toluene may be present, although the presence of this solvent is said to be not required. The reason for utilizing this type of reactant, that is, a compound containing a tertiary alpha-carbon atom is that, in the past, it has been generally accepted that only those formimines in which the amino group is attached to a tertiary carbon atom will be sufficiently stable for isolation and for further reaction.
In contradistinction to the teachings set forth in the above-cited reference, it has now been discovered that formimines which have been prepared from alkyl amines where the alpha-carbon atom (the carbon atom directly bonded to the nitrogen atom) is primary or secondary may be utilized in a reaction with an aromatic amine to form the desired products of the present invention, that is, aromatic diamines. Formimines derived from such amines will hereinafter be referred to as primary and secondary alkyl formimines. In the case of primary alkyl formimines, the alpha-carbon atom directly bonded to the nitrogen atom possesses two hydrogen atoms while in the case of the secondary alkyl formimines the alpha-carbon atom possesses only one hydrogen atom.
This invention relates to the formation of aromatic diamines, and more specifically to the formation of the aforementioned diamines by reacting a primary or secondary alkyl formimine with a tertiary aromatic amine in an anhydrous medium.
The compounds of the present invention which comprise aromatic diamines will find a wide variety of uses as antioxidants or antiozonants for various organic substrates such as petroleum products such as heating oil, lubricating oil, gasoline, etc., or other products which are subjected to the action of oxygen or ozone such as natural rubber, synthetic rubber such as Buna S, etc. In addition, these compounds may also find use in the chemical industry as herbicides, fungicides, insecticides, etc.
It is therefore an object of this invention to provide a process for obtaining aromatic diamines, and particularly alkyl-substituted aromatic diamines.
A further object of this invention is to provide a process for obtaining aromatic diamines in which the reactants form the desired product in an anhydrous acidic medium.
In one aspect an embodiment of this invention resides in a process for the preparation of an aromatic diamine which comprises reacting a primary or secondary formimine, which is prepared by reacting a linear or branched chain primary alkyl amine with a formaldehyde to form said formimine reactant characterized by possession of a linear or branched chain alkyl moiety attached to the nitrogen atom of said formimine reactant, with a tertiary aromatic amine in an anhydrous acidic medium, and recovering the resultant aromatic diamine.
A specific embodiment of this invention is found in a process for the preparation of an aromatic diamine which comprises reacting formaldehyde with n-hexylamine at a temperature in the range of from about 20.degree. to about 100.degree. C. and a pressure in the range of from about atmospheric to about 100 atmospheres, reacting the resultant n-hexylformimine with N,N-dimethylaniline at a temperature in the range of from about 20.degree. to about 100.degree. C. and a pressure in the range of from about atmospheric to about 100 atmospheres in the presence of anhydrous trifluoroacetic acid, and recovering the resultant p-dimethylamino-N-n-hexylbenzylamine.